Experimental assessment of oxygen exchange capacity and thermochemical redox cycle behavior of Ba and Sr series perovskites for solar energy storage

• BaBO3 and SrBO3 perovskites in solar thermochemical (ST) energy storage are studied.
• Co-based perovskites are promising candidates for ST energy storage.
• BaCoO3 shows the best O2 exchange capability.
• Multi O2 exchange stages of perovskites in redox process are observed.

Thermochemical redox processes involving novel oxygen ion conducting materials with perovskites structure are studied to evaluate their application potential for solar energy storage in concentrated solar power plants. A series of Ba and Sr containing perovskites was synthesized via modified Pechini method and their crystal structure was characterized by XRD. The thermochemical reduction–oxidation steps of the redox cycle and oxygen exchange capacity of the perovskites were investigated by thermogravimetric (TG) analysis. The results revealed that Co-based perovskites are the most promising candidates for solar thermochemical energy storage application. The O2 release/absorption of Co-based perovskites is completed in a reversible way when reaching a given temperature. BaCoO3 reduction occurs promptly when the temperature reaches 900 °C in Ar atmosphere (pO2 = 10−6 atm), and the oxidation proceeds completely as soon as the gas is switched from Ar to 20% O2 at 600 °C. In these conditions, the amount of monatomic oxygen released/captured reaches 0.47/0.49 mol per mol BaCoO3. Part substitution in A-site improves the O2 exchange capacity of Ba0.5Sr0.5FeO3−δ but not Ba0.5Sr0.5CoO3−δ, while part substitution in B-site improves the O2 exchange capacity of SrCo0.8Fe0.2O3−δ and SrCo0.2Fe0.8O3−δ. Part substitution together in A-site and B-site of perovskites does not improve the O2 exchange capacity of Ba0.5Sr0.5Co0.8Fe0.2O3−δ and Ba0.5Sr0.5Co0.2Fe0.8O3−δ. The Fe-based perovskites generally exhibit continuous non-stoichiometry changes according to the temperature change suggesting continuous topotactic evolution, while the non-stoichiometry of Mn-based systems is almost not changed at the considered temperatures. Ba containing systems (BaCoO3, BaFeO3 and Ba0.5Sr0.5CoO3) show the largest oxygen release ability under inert (pO2 = 10−6 atm) or oxidizing atmosphere (pO2 = 0.2 atm) up to 1050 °C, while only BaCoO3 can be fully re-oxidized at 600 °C in a 20% O2 atmosphere, with an energy storage capacity of 292 J/g.